Means for controlling the voltage of discharge devices



30, 1938- H. H. RENNER 2,128,562

MEANS FOR CONTROLLING THE VOLTAGE OF DISCHARGE DEVICES Filed Jan. 9, i954 Fig. I.

I \IZ lNVENTOR' HTTORNEY Patented Aug. 30, 1938 MEANS FOR CONTROLLING THE VOLTAGE OF DISCHARGE DEVICES Hans Helmut Renner, Frankfort-on-the-Main, Germany Application January 9,

1934, Serial No. 705,977

In Great Britain January 10, 1933 Claims.

This invention relates to means for controlling the voltage or current of mercury arc converters or like discharge devices and particularly to means of the kind comprising a grid or control electrode to which an alternating voltage is applied that attains a critical or starting value at an instant adjustable relatively to the anode voltage. The characteristics of a discharge device may be such that at the rated voltage of the device no discharge will occur unless during the half cycle that the anode is positive, the grid is raised to a positive potential relatively to the cathode defined by a curve of critical potential which represents for each instant of anode voltage the minimum positive grid potential that will start the are. On the other hand the characteristics of the device may be such that at the rated voltage of the device discharge occurs during the half cycle that the anode is positive unless starting of the arc is prevented by maintaining the grid at a potential sufficiently low or sufrlciently negative to the cathode defined by a curve of critical potential which represents for each instant of anode voltage the minimum negative potential or the maximum positive potential that can be applied to the grid without the occurrence of starting of the are. It has previously been proposed to effect regulation by varying the amplitude of an alternating voltage of frequency maximum control that can be exerted extends over somewhat less than one half of the positive half cycle and at least over a part of the range the control exerted tends to be somewhat indefinite. It has also been proposed to exert control by varying the phase relationship between the anode voltage and an alternating or pulsating grid potential which has the same frequency as the anode voltage. In such manner regulation may be eiiected over the whole half cycle but the phase displacemnt calls for apparatus with means such as windings that may be relatively rotated or rotary switching devices. An object of the invention is the provision of an alternative method for efiecting control in a definite manner. Another object is the provision of apparatus whereby the control may be exerted over a substantial part of the half cycle.

In means for controlling the voltage or current of a mercury are or other converter comprising a grid or control electrode to which an alternating voltage is applied that attains a critical or starting value at an instant adjustable relatively to the anode voltage, according to the present invention the adjustment is made by equal to the anode voltage, but in this way the varying the value of a third harmonic forming part of an alternating voltage wave which is of frequency equal to that of the anode voltage and which is impressed upon the grid.

The alternating voltage wave applied to the grid is derived by adding to a fundamental voltage wave a third harmonic by means through which the amplitude and direction of the third harmonic may be adjusted.

One arrangement of mercury arc rectifier in accordance with the invention will now be described, by way of example, with reference to the accompanying diagrammatic drawing of which Figure 1 shows an arrangement of a single phase rectifier and Figure 2 grid potential curves produced by this arrangement.

rectifier I is of single In the drawing, the phase construction and at the rated voltage of the rectifier the arc will strike over the greater part of the anode positive half cycle unless the grid is negative or is less positive than values defined by a critical voltage curve l6 appreciably above and nearly parallel with the line of zero voltage.

The anode 2 of the r ectifier I is connected to one phase of a three phase power supply 5 and the cathode 3 is conne cted through the load 4 to another phase of the supply 5. The primary 6 of a bias transformer 1 is connected across two of the said phases secondary winding 8 of and one terminal of the the transformer l is connected to the grid 9 of the rectifier whilst the other terminal of the said winding is connected to a sliding contact adapted to traverse a re point whereof is conne II or equivalent means sistor device In, the midcted with the cathode 3 of the rectifier over a line I2.

A current derived from the secondary windings M connected in open delta, of a three phase transformer l3 connected with the power supply 5, the core of which transformer is saturated during operation, passes through the resistor device. Thus a current having a frequency thrice that of the power supply flows through the resistor device.

When the sliding contact II is in the midposition of the resistor substantially pure sine device ill a potential of wave form is applied to the grid 9. The wave is represented on Figure 2 at I5. The potential is in phase with the anode age curve I6 determine the are.

S the t me str ing o If the sliding contact H is moved in one direction from the mid-point of the resistor device ill, the potential impressed on the grid 9 includes a third harmonic component which tends to give a resulting potential curve l8 with two humps I9, 20, the said curve cutting the critical voltage curve H at 2|. The result is that the curve slopes up more steeply from the zero line and the arc strikes at an earlier period, the degree to which the striking is expediated depending upon the position of the contact II and the amplitude of the third harmonic.

If, on the other hand, the sliding contact H is moved in the other direction from the mid-point the potential impressed on the grid includes a third harmonic component which tends to give the potential curve a central hump, as shown in curve 22, cutting curve H5 at 23. The result is that the curve slopes up less steeply from the zero line and the arc strikes at a later period, the degree to which the striking is retarded depending upon the position of the contact and the amplitude of the third harmonic.

The grid voltage will not in every case be in phase with the anode voltage, but will be arranged to suit the type of transformer connection employed for the rectified and the range of control required.

I claim: r

1. Means for controlling the output of a vapour electric converter associated with an alternating voltage circuit of the kind including a cathodic electrode, an anodic electrode and a control elec trode to which control electrode is applied an alternating voltage that attains a critical or starting value at a prearranged instant, comprising means adapted to provide a potential including an alternating voltage of sine wave form having a periodicity equal to that of the voltage of the said circuit and the third harmonic of the said alternating voltage, a transformer connected in said control circuit, said transformer having a saturable core and an open delta secondary winding including a resistor device, said resistor device being connected across said transformer secondary between said control electrode and the cathode electrode by a center tapping and an adjustable. tapping, the latter being arranged to adjust the value of the third harmonic present in said potential.

2. In combination, a plurality of electric circuits, including an alternating supply circuit and a direct current power circuit, a vapor electric converter interconnecting said circuits, said converter having cathode, anode and grid electrodes, a grid circuit for said converter for supplying the grid electrode with alternating potential of the same phase as the supply circuit, a circuit including wave-form control means comprising a variable resistor device cooperating with a saturated transformer for imposing on said grid circuit a third harmonic component which in combination with said component of the same phase as the supply circuit is adapted to control the power transmitted by the converter, the waveform resulting from the two components having a decided peak, and means for varying the amount and direction of flow of the component from said resistor device for varying the position of said peak relative to the neutral line of the wave.

' 3. Means for controlling the output of a vapor electric converter having anode, cathode and control electrodes and taking operating current from an alternating current supply circuit, comprising a voltage transformer connected across the alternating current circuit and arranged to provide a fundamental sine wave voltage for said control electrode with a periodicity equal to that of the supply circuit, a three phase transformer connected across said alternating supply circuit for providing a third harmonic voltage, and adjustable means for the third harmonic voltage comprising a resistor device connected across the secondary of the three phase transformer and centrally connected to said cathode while the voltage transformer supplying the fundamental sine wave voltage is connected to the control electrode by a tapping adjustable relatively of the resistor device for varying the amplitude and phase of the third harmonic voltage applied to the fundamental sine wave voltage and controlling the discharge between the anode and cathode.

4. Means for controlling the output of a vapor electric converter having anode, cathode and control electrodes, comprising a three phase alterhating current supply, said converter being connected to one phase of said three phase supply, a single phase transformer connected across one phase of said supply and arranged to supply said control electrode with alternating current voltage of the same sine wave form and frequency as said supply, a three phase transformer connected across said supply and arranged to provide a third harmonic alternating current voltage of sine wave form but at three times the frequency of the supply, a resistor device in circuit with said three phase transformer comprising a resistor having a central tapping connection with the cathode electrode and an adjustable tapping connection through said, single phase transformer to the control electrode arranged for adjustment relative to the resistor on either side of said central tapping for varying the wave peak of the voltage on the control electrode and controlling the discharge between the anode and cathode of the converter,

5. Means for controlling the output of a vapor electric converter having anode, cathode and control electrodes,,comprising a three phase alternating current supply, said converter being connected to one phase of said three phase supply, a single phase transformer connected across one phase of said supply and arranged to supply said control electrode with alternating current voltage of the same sine wave form and frequency as said supply, a three phase, transformer connected across said supply and arranged to provide a third harmonic alternating current voltage of sine wave form but at three times the frequency of the supply, a resistor device in circuit with said three phase transformer, comprising a resistor having a central tapping connected with the cathode electrode and a tapping connected with the control electrode and movable along the resistor on one side or the other of said central tapping to vary the amplitude and from one side to the other for inverting the phase of the sine wave of the third harmonic for varying the wave peak of the voltage on the control electrode and controlling the discharge between the. anode and cathode of the converter.

HANS HELMUT RENNER. 

